Method of forming carbon coating



Jan. 26, 1965 H. s. SPACIL 3,167,449

METHOD OF FORMING CARBON COATING Filed April 26, 1961 POWER $0 (/ECE 26[n vervzfior: Henry S. SpdC/Y,

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3,167,449 METHQI) F FORMING CARBON COATING Henry S. Spacil, Schenectady,N.Y., assignor to General Electric Company, a corporation of New YorkFiled Apr. 26, 1951, Ser. No. 105,762 8 Claims. (Cl. 111-200) Thisinvention relates to composite articles and to methods of formingcomposite articles and more particularly to composite articles andmethods of forming composite articles having a member with a lowdensity, non-porous carbonaceous coating thereon.

Carbonaceous coatings are desirable to provide wear and abrasionresistant surfaces for members. For example, such coatings would beadvantageous for covering bearing members. These coatings would alsohave application to zirconium process tubes which are employed in theatomic energy industry. Such coated tubes would prevent hydrogen pickupby the zirconium since gas transfor would not be possible through thenonporous coating.

Carbon-aceous gases have been thermally decomposed and deposited on asurface to produce pyrolytic graphite. As a result of the decomposition,carbon is removed from the gas and deposits on the surface so thatplanar graphite crystallites are aligned into a layer structure. Itwould be desirable to provide composite article having a member with asmooth, adherent, carbonaceous coating which has a low density, isnon-porous, and is continuous. Furthermore, it would be advantageous toprovide deposition methods of forming such composite articles.

It is an object of my invention to provide a deposition method offorming adherent, smooth, continuous carbonaceous coatings on members.

It is another object of my invention to provide a deposition method offorming such carbonaceous coatings with a low density.

It is a further object of my invention to provide a deposition method offorming such carbonaceous coatings which are non-porous.

It is a still further object of my invention to provide a compositearticle having a member with an adherent, smooth, non-porous, continuouscarbonaceous coating thereon.

In carrying out my invention in one form, a method of depositing anadherent carbonaceous coating on a member comprises providing a chamber,positioning an electrically conductive member Within the chamber, themember having a similar coetficient of expansion to said coating,positioning an anode within the chamber surrounding and spaced from themember, evacuating the chamber, supplying a mixture of hydrocarbon gasand a gas selected from the group consisting of argon, helium, hydrogen,argon and hydrogen, and helium and hydrogen to the chamber, and applyinga discharge within the chamber whereby a carbonaceous coating isdeposited on the member, the discharge having a current density of 15milliamperes per square centimeter to 500 milliamperes per squarecentimeter.

These and various other objects, features and advantages of theinvention will be better understood from the following description takenin connection with the accompanying drawing in which:

The single figure is a sectional View of a deposition apparatus forforming carbonaceous coating in accordance with my invention.

In the single figure of the drawing, a deposition apparatus is showngenerally at 10 which comprises a metallic chamber 11 including acylindrical body portion 12 and end closure plates 13. A flange 14 islocated at each end of body portion 12 to which an associated plate 13is fastened by means of bolts 15 extending through apertime PatentedJan. 26, 1965 tures in both the flange and plate. In one end plate 13,an aperture 16 is located in which an inlet tube 17 is posi tioned andextended to gas sources (not shown). Suitable gas sources, inlet linesand valves (not shown) are provided for supplying, regulating and mixingthe gases. In the other end plate 13, an aperture 18 is located in whicha tube 19 is positioned and extended to pump 20 for evacuating chamber11. An electrically conductive member 21 having a similar coefficient ofexpansion to the layer to be deposited is positioned within the chamberas a cathode and supported therein by any suitable means (not shown). Ihave found that molybdenum, zirconium, graphite and tungsten aresuitable materials for member 21 which can be of various configurationssuch as sheet, rod, tube, or wire. An anode 22, for example of copper,nickel or molybdenum, is shown in the form of a wire mesh screensurrounding member 21 within chamber 11. Other metallic anodes can beemployed providing that the material does no contaminate the apparatusor melt at operating temperatures. An electrical lead 23 is secured tomember 21 While an electrical lead 24 is secured to anode 22 throughinsulating Washers 25 positioned in one of the end closure plates 13.Leads 23 and 24 are connected to a suitable direct current power source26. A resistance 27 is provided between power source 25 and lead 24 toregulate the current flow.

I discovered unexpectedly that adherent, smooth, continuous carbonaceoucoatings with low density and nonporous are produced on a member to forma composite article by positioning an electrically conductive member,such as a molybdenum, zirconium, graphite, or tungsten member Within achamber, the member having a similar coefficient of expansion to thecoating to be deposited, positioning an anode within the chambersurrounding and spaced from the member, evacuating the chamber,supplying a mixture of hydrocarbon gas and a gas selected from the groupconsisting of argon, helium, hydro gen, argon and hydrogen, and heliumand hydrogen to the chamber, and applying a discharge within thechamber, the discharge having a current density of 15 milliamperes persquare centimeter to 500 milliamperes per square centimeter.

I found further that it was preferable to clean the member initially bysupplying a gas selected from the group consisting of argon andhydrogen, helium and hydrogen, and hydrogen to the evacuated chamberwhile supplying voltage in the range of 200 to 300 volts to produce acurrent density of 30-100 milliamperes per square centimeter. Duringsubsequent actual deposition, 200 to 750 volts provides the requiredcurrent density of 15 milliamperes per square centimeter to 500milliamperes per square centimeter. The current supplied by the powersource heats the member to a temperature in the range of 600 C. to 1200C. with a preferred temperature of 600 C. to 800 C. during deposition.At temperatures below 600 C. the rate of deposition drops offdrastically while at temperatures above 1200 C. the coating changes to amore crystalline structure.

I found also that the chamber should be evacuated to a pressure of about2 millimeters of mercury to 50 centimeters of mercury. The hydrocarbongas is decomposed to carbon and hydrogen. The carbon atoms arepositively charged by the discharge to carbon ions which are attractedto member 21, the cathode. The carbon is deposited on member 21 as anadherent, smooth and continuous coating. The argon or helium stabilizesthe discharge and prevents arcing whereby higher current densities canbe employed. The hydrogen revents too rapid decomposition of thehydrocarbon gas which would result in sooting.

In the operation of the disposition apparatus in the single figure ofthe drawing, chamber 11 is evacuated to a pressure of 2 millimeters ofmercury to 50 centimeters of mercury. A gas selected from the groupconsisting of argon and hydrogen, helium and hydrogen, and hydrogen issupplied through inlet line 17 to chamber 11 to remove impurities frommember 21.

the range of 200 volts to 300 volts which produces a current density of30 milliampers per square centimeter to 100 milliampers per squarecentimeter. A hydrocarbon gas, such as methane or acetylene, is mixedwith a gas selected from the group consisting of argon, helium, argonand hydrogen, and helium and hydrogen and supplied through inlet tube 17to chamber 11. Power is supplied to leads 23 and 24 from power source 26to provide a voltage in the range of 200'volts to 750 volts whichproduces a current density of milliampers per square centimeter to 560milliampers per square centimeter. The current supplied by the powersource heats member 21 to a temperature in the range of 600 C. to 1200"C. with a preferred range'ot 600 C. to 800 C. during deposition. Thecarbon atoms which are decomposed from the hydrocarbon gas arepositively charged by the discharge and attracted to member 21 todeposit a carbonaceous layer thereon. The layer is adherent, smooth andcontinuous. it has a low density of about 1.3 gin/cm. and is non-porous.Pump 26 maintains the desired low pres sure in chamber 11 while itremoves the products of the reaction therefrom and an adherent, smooth,non-porous,

continuous carbonaceous coating is formed on the member.

Several examples of carbonaceous coatings which were made in accordancewith the methods of the present invention are as follows:

Example I A deposition apparatus was set up generally in accordance withthe single figure of the drawing. A molybdenum sheet having a length of3 inches, a width of 1 inch and a thickness of about mils was suspendedwithin the chamber of as the cathode. A molybdenum mesh screensurrounded and was spaced uniformly from the sheet to provide an anode.A mixture of argon and hydrogen was supplied to the chamber which wasevacuated to a pressure of about 15 millimeters of mercury. The powersource supplied current through the leads to provide a current'densityof 45 milliamperes per square centimeter. This cleaning of the cathodewas continued for 5 minutes to remove impurities from the molybdenumsheet. Acetylene gas was then supplied to the chamber and the gasesadjusted to provide a mixture of 1 part of acetylene, 1 part of argonand 4 parts of hydrogen. The deposition was continued for about 40minutes at a pressure of about 15 millimeters of mercury and a currentdensity of 15 milliamperes per square centimeter. The molybdenum sheetwas heated to 700 C. The sheet had an adherent, smooth, non-porous,continuous carbonaceous coating of 5 mils thickness. The coating had adensity of about 1.3 grams per cubic centimeter.

Example 11 A deposition apparatus was set up generally in accordancewith the single figure of the drawing. A graphite rod having a length of3 inches and a diameter of inch was suspended within the chamber as thecathode. A molybdenum mesh screen surrounded and was spaced uniformlyfrom the sheet to provide an anode. A mixture of argon and hydrogen wassupplied to the chamber which was evacuated to a pressure of about 15millimeters of mercury. The power source supplied current through theleads to provide a current density of milliamperes per squarecentimeter. This cleaning of the cathode was continued for 5 minutes toremove impurities from the graphite rod. Acetylene gas was then suppliedto the chamber and the gases adjusted to provide a mixture of 1 Power issupplied to leads '23 and 24 from power source 26 to provide a voltagein part of acetylene, 1 part of argon and 4 parts of hydrogen. Thedeposition was continued for about 40 minutes at a pressure of about 15millimeters of mercury and a density of 15 milliampers per squarecentimeter. The graphite rod was heated to 700 C. The rod had anadherent, smooth, non-porous, contitnuous carbonaceous coating of 5 milsthickness. The coating had a density of about 1.3 grams per cubiccentimeter.

Example III A deposition apparatus was set up generally in accordancewith the single figure, of the drawing. A zirconium sheet having alength of 3 inches, a width of 1 inch and a thickness of about 40 milswas suspended within the chamber as the cathode; A molybdenum meshscreen surrounded and was spaced uniformly from the sheet to provide ananode. A mixture of argon and hydrogen was supplied to the chamber whichwas evacuated to a pressure of about 15 millimeters of mercury. Thepower source supplied current through the leads to provide a currentdensity of 45 miliiampers per square centimeter.

This cleaning of the cathode was continued for 5 minutes to removeimpurities from the zirconium sheet. Acetylene gas was then supplied tothe chamber and the gases adjusted to provide a mixture of 1 part ofacetylene, 1 part of argon and 4 parts of hydrogen. The deposition wascontinued for about 40 minutes at a pressure of about 15 millimeters ofmercury and a current density of 15 miiliamperes per square centimeter.The zirconium sheet was heated to' 700 C. The sheet had an adherent,smooth, non-porous, continuous carbonaceous coating of 5 mils thickness.The coating had a density of about 1.3 grams per cubic centimeter.

Example IV ance with the single figure of the drawing. A rolled-up tubeof tungsten having a length of 2 inches, and a thickness of 5 mils wassuspended within the chamber as the cathode. A molybdenum mesh screensurrounded and was spaced uniformly from the sheet to proved an anode. Amixture of argon and hydrogen was supplied to the chamber which wasevacuated to a pressure of about 15 millimeters of mercury. The powersource supplied current through the leads to provide a current densityof 45 milliamperes per square centimeter. This cleaning of the cathodewas continued for 5 minutes to remove impurities from the tungsten tube.Acetylene gas was then supplied to the chamber and the gases adjusted toprovide a mixture of 1 part of acetylene, 1 part of argon and 4 parts ofhydrogen. The deposition was continued for about 40 minutes at apressure of about 15 millimeters of mercury and a current density of 15milliamperes per square centimeter. The tungsten tube was heated to 700C. The sheet had an adherent, smooth, non-porous, continuouscarbonaceous coating of 5 mils thickness. The coating had a density ofabout 1.3 grams per cubic centimeter.

Example V A deposition apparatus was set up generally in accordance withthe single figure of the drawing. A tungsten wire having a length of 3inches, and a diameter of 10 mils was suspended within thechamber as thecathode.- A molybdenum mesh screen surrounded and was spaced uniformlyfrom the sheet to provide an anode. Hydrogen was supplied to the chamberwhich was evacuated to a pressure of about 15 millimeters of mercury.The power source supplied current through the leads to provide a currentdensity of 45 miiliamperes per square centimeter. This cleaning of thecathode was continued for 3 minutes to remove impurities from thetungsten wire. Acetylene gas was then supplied to the chamber and thegases adjusted to provide a mixture of 1 part of methane and 5 parts ofhydrogen. The deposition was continued for 5 minutes at a pressure ofabout millimeters of mercury 5 and a current density of 250 milliamperesper square centimeter. The tungsten wire was heated to 1100" C. Thesheet had an adherent, smooth, non-porous, continuous carbonaceouscoating of 3 mils thickness.

While other modifications of this invention and variation in the methodwhich may be employed within the scope of the invention have not beendescribed, the invention is intended to include such that may beembraced Within the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method of depositing an adherent carbonaceous coating on a memberwhich comprises providing a chamber, positioning an electricallyconductive member within said chamber, said member having a similarcoefiicient of expansion to said coating, positioning an anode withinsaid chamber surrounding and spaced from said member, evacuating saidchamber, supplying a mixture of hydrocarbon gas and a gas selected fromthe group consisting of argon, helium, hydrogen, argon and hydrogen, andhelium and hydrogen to said chamber, and applying a discharge withinsaid chamber whereby a carbonaceous coating is deposited on said member,said discharge having a current density of 15 miliiamperes per squarecentimeter to 500 milliamperes per square centimeter.

2. The invention as claimed in claim 1 wherein said electricallyconductive member is molybdenum.

3. The invention as claimed in claim 1 wherein said electricallyconductive member is graphite.

4. The invention as claimed in claim 1 wherein said electricallyconductive member is zirconium.

5. The invention as claimed in claim 1 wherein said electricallyconductive member is tungsten.

6. A method of depositing an adherent carbonaceous coating on a memberwhich comprises providing a chamber, positioning an electricallyconductive member Within said chamber, said member having a similarcoefficient of expansion to said coating, positioning an anode withinsaid chamber surrounding and spaced from said member, evacuating saidchamber, supplying a mixture of hydrocarbon gas and a gas selected fromthe group consisting of argon, helium, hydrogen argon and hydrogen, andhelium and hydrogen to said chamber, and applying a direct currentpotential between said anode and said member to heat said member to atemperature in the range of 600 C. to 1200 C. whereby a carbonaceouscoating is deposited on said member.

7. A method of depositing an adherent carbonaceous coating on a memberwhich comprises providing a chamber, positioning an electricallyconductive member Within said chamber, said member having a similarcoefiicient of expansion to said coating, positioning an anode Withinsaid chamber surrounding and spaced from said member, evacuating saidchamber, supplying a mixture of hydrocarbon gas and a gas selected fromthe group consisting of argon, helium, hydrogen, argon and hydrogen, andhelium and hydrogen to said chamber, and applying a direct currentpotential between said anode and said member to heat said member to atemperature in the range of 600 C. to 800 C. whereby a carbonaceouscoating is deposited on said member.

8. A method of depositing an adherent carbonaceous coating on a memberwhich comprises providing a chamber, positioning an electricallyconductive member within said chamber, said member having a similarcoefficient of expansion to said coating, positioning an anode Withinsaid chamber surrounding and spaced from said member, evacuating saidchamber, supplying a gas selected from the group consisting of argon andhydrogen, helium and hydrogen, and hydrogen to said chamber, applying adischarge having a current density of 30 milliamperes per squarecentimeter to milliamperes per square centimeter within chamber toremove impurities from said member, supplying a mixture of hydrocarbongas and a gas selected from the group consisting of argon, helium,hydrogen, argon and hydrogen, and helium and hydrogen to said chamber,and applying a discharge within said chamber whereby a carbonaceouscoating is deposited on said member, said discharge having a currentdensity of 15 milliamperes per square centimeter to 500 milliamperes persquare centimeter.

References Cited by the Examiner UNITED STATES PATENTS 261,741 7/82Maxim 11849.1 X 1,813,514 7/31 Schmidt et al. 204--173 2,572,851 10/51Gardner 204-173 2,635,994 4/53 Tierman 204-173 2,817,605 12/57 Sanz etal l17-228 2,853,969 9/58 Drewett 117226 X RICHARD D. NEVIUS, PrimaryExaminer.

I. B. SPENCER, Examiner.

1. A METHOD OF DEPOSITING AN ADHERENT CARBONACEOUS COATING ON A MEMBERWHICH COMPRISES PROVIDING A CHAMBER, POSITIONING AN ELECTRICALLYCONDUCTIVE MEMBER WITHIN SAID CHAMBER, SAID MEMBER HAVING A SIMILARCOEFFICIENT OF EXPANSION TO SAID COATING, POSITIONING AN ANODE WITHINSAID CHAMBER SURROUNDING AND SPACED FROM SAID MEMBER, EVACUATING SAIDCHAMBER, SUPPLYING A MIXTURE OF HYDROCARBON GAS AND A GAS SELECTED FROMTHE GROUP CONSISTING OF ARGON, HELIUM, HYDROGEN, ARGON AND HYDROGEN, ANDHELIUM AND HYDROGEN TO SAID CHAMBER, AND APPLYING A DISCHARGE WITHINSAID CHAMBER WHEREBY A CARBONACEOUS COATING IS DEPOSITED ON SAID MEMBER,SAID DISCHARGE HAVING A CURRENT DENSITY OF 15 MILLIAMPERES PER SQUARECENTIMETER TO 500 MILLIAMPERES PER SQUARE CENTIMETER.